1. Field of the Invention
The invention relates to a sheet supplying apparatus provided with a plurality of sheet decks stacking various sheets thereon and capable of supplying many kinds of sheets, and an image forming system provided with the sheet supplying apparatus and for forming images on the many kinds of sheets supplied from the sheet supplying apparatus, and providing the sheets in the form of bundle to a user.
2. Description of Related Art
(First Example of the Conventional Art)
Fields related to digital copying machines and printing include a field called on-demand print, and in recent years, this field has been attracting attention. The on-demand print can meet many kinds and small lots of demands on demand from customers, and facilitates the alteration of contents, and is suited for the production of documents such as manuals and pamphlets for individuals. Also, the on-demand print facilitates the alteration of contents and can therefore greatly curtail the stock of printed documents or the like. Further, the on-demand print can accomplish the great shortening of the number of steps and time by data inputting to the completion of bookbinding being effected by in-line, the great shortening of the time limit of delivery and the curtailment of delivery cost based on the ease of data forwarding by customers and a digital circuit being connected together.
An image forming apparatus such as a digital copying machine which has realized such an on-demand print technique is improved in its quality of image to a level approximate to printed matter by the recent heightening of the quality of image, and has come to be used for the printing of pamphlets such as catalogs and manuals of products, or pamphlets such as distributed matter in offices or the like.
Image forming systems using an image forming apparatus such as a copying machine coping with the on-demand print include what has been proposed as a large-sized image forming system for executing, by a series of job operations, such post-treating processes as the Z fold process of receiving the supply of sheets from a sheet supplying apparatus of large capacity, and folding a sheet fed out from the image forming apparatus into a substantially Z-shape (for example, the folding process of folding A3 size into A4 size, and thereafter folding one portion of A4 size into a half), the inserter process of inserting a different kind of sheet between the sheets, the stapling process of stapling a bundle of sheets, the punching process of punching the bundle of sheets, and the bookbinding process, in order to cope with a variety of sheets.
The sheet supplying apparatus, as is disclosed in Japanese Patent Application Laid-Open No. 2001-506212, is formed by a plurality of sheet decks stacking different kinds of sheets thereon being connected in series (in tandem). A variety of sheets include sheets differing in size, thickness, material, etc.
(Second Example of the Conventional Art)
There is also such a system printer as described in Japanese Patent Application Laid-Open No. H01-209235. That is, there is also a system printer in which prior to the supply of sheets from a sheet tray which is the sheet stacking means of a sheet deck provided with a relatively long conveying path and connected, a sheet is preliminarily conveyed to just before a position which first joins another sheet conveying path to thereby keep the order of sheet conveyance to an image forming portion, and yet shorten the sheet conveying distance to the image forming portion, thereby improving productivity.
(Problems Peculiar to the First Example of the Conventional Art)
The image forming system in which the sheet decks of the sheet supplying apparatus of large capacity are connected in series (in tandem) shares a sheet conveying path from each sheet deck to the image forming apparatus, and therefore has suffered from the following problems.
For example, in the job of preparing a bundle of sheets having different kinds of sheet mixed in one and the same bundle of sheets, it sometimes happens that due to the changing of the kind of the sheet, the sheet deck for supplying the sheets is changed from a sheet deck nearest to the image forming apparatus to a sheet deck farthest from the image forming apparatus. In such case, if the sheets are supplied from the sheet deck to the image forming apparatus at ordinary sheet supply timing, the farthest sheet deck, which has a long sheet conveying path, supplies a sheet at an interval corresponding to the long conveying distance, with respect to a sheet supplied from the nearest sheet deck. This has led to the problem that the image forming timing of the image forming apparatus becomes late and the productivity of the image forming system is lowered.
In order to cope with this problem, there is conceivable the conveyance control of changing the sheet supply timing with the number of the connected sheet decks or the connection and disposition of the sheet decks taken into account, or accelerating the sheets in the sheet conveying path to thereby shorten the inter-sheet interval, but in this case, there may arise another problem that the conveyance control becomes complicated.
(Problem Peculiar to the Second Example of the Conventional Art)
The system printer according to the second example of the conventional art suffers from the problem that only one sheet deck can be connected thereto and the kinds of the sheets are limited.